Current typical methods to realize nuclear-nuclear quantum gates require a sequence of electron-nuclear quantum gates by using dynamical decoupling techniques, which are implemented at low temperature because of the short decoherence and relaxation time of the nitrogen-vacancy (NV) spin at room temperature. This limitation could be overcome by using periodic resets of an NV spin as a mediator of the interaction between two nuclear spins [Q. Chen et al., Phys. Rev. Lett. 119, 010801 (2017)]. However, this method works under stringent coupling strength conditions, which makes it not applicable to heteronuclear quantum gate operations. Here we develop this scheme by using radio-frequency fields to control different nuclear-spin species. Periodic resets of the NV center protect the nuclear spins from decoherence and relaxation of the NV spin. Radio-frequency control provides the probability to have highly selective and high-fidelity quantum gates between heteronuclear spins and detecting nuclear spins by using a nuclear-spin sensor under ambient conditions.

In this work, $\pi , {\sigma }^{+}$, and ${\sigma }^{-}$ transitions between magnetic sublevels of the $D_1$ line of all alkali-metal atoms are considered analytically. General block Hamiltonian matrices in the presence of a magnetic-field for the ground and excited states are built in order to describe all the transitions. Eigenvalues and eigenkets describing ground and excited levels are calculated and modified and unperturbed transfer coefficients as a function of the nuclear spin $I$, the magnetic quantum number $m$, and the magnetic-field magnitude $B$ are defined. Transition cancellations are observed only for some $\pi$ transitions of each isotope. The main result is that we obtain a single formula which expresses the magnetic-field values canceling these transitions. These values also correspond to the case when the intensities of some of the other transitions reach their maximum. In addition, we examine the derivative of $\pi$ transition modified transfer coefficients in order to find the magnetic-field values which correspond to the intensities' maximum. The accuracy of the magnetic-field $B$ values is only limited by the uncertainty of the physical quantities involved.

The chiral transfer of quantum information in a metal nanoring network is presented. A system of three metal nanorings coupled to a two-level quantum dot enables the chiral transport of quantum states by breaking the time-reversal symmetry, which provides a platform for chiral quantum information processing in nanorings. The direction of the chirality can be controlled by preparing the quantum dot in its ground or excited state. We show that the system dynamics can be controlled such that one can achieve a perfect or a partial chiral transfer of the excitation. The synthetic magnetic field that enables the chirality in the system makes the generation of specifically tailored entangled nanoring states possible. As particular examples, we show that in this platform the generation of a two-excitation NOON state and entangled coherent states among nanorings can be realized.

Currently, existing quantum annealers have proven themselves as viable technology for the first practical applications in the noisy-intermediate-scale-quantum era. However, to fully exploit their capabilities, a comprehensive characterization of their finite-time excitations is instrumental. To this end, we develop a phase diagram for driven Ising chains, from which the scaling behavior of the excess work can be read off as a function of process duration and system size. “Fast” processes are well described by the Kibble-Zurek mechanism; “slow” process are governed by effective Landau-Zener dynamics; and “very slow” processes can be approximated with adiabatic perturbation theory.

One hurdle to performing reliable quantum computations is overcoming noise. One possibility is to reduce the number of particles needing to be protected from noise and instead use systems with more states, so-called qudit quantum computers. In this paper we show that codes for these systems can be derived from already known codes, and, in particular, that degenerate stabilizer codes can have their distance also promised upon sufficiently large local dimension as well as an alternative bound on the local dimension required to preserve the distance of local-dimension-invariant codes, which is a result which could prove to be useful for error-corrected qudit quantum computers.

We present a study of the Rydberg spectrum in ${}^{39}\mathrm{K}$ for $nS$ and $n{D}_{3/2}$ series connected to $5{}^2{P}_{1/2}$ using two-photon spectroscopy based on electromagnetically induced transparency in a heated vapor cell. We observed some 80 transitions from $5P_{1/2}$ to Rydberg states with principal quantum numbers $n\sim 50–90$, and determined their transition frequencies and state energies with sub-GHz precision. Our spectroscopy results lay the groundwork for using Rydberg atoms as sensitive microwave photon detectors in searches for dark matter axions in the $\sim 40–200 \mu \mathrm{eV}$ mass range, which is a prime range for future axion searches suggested by theory studies.

We study the process of laser-assisted charge transfer in collisions of positronium atoms with protons (antiprotons) with formation of Rydberg hydrogen (antihydrogen) atoms by the use of classical trajectories Monte Carlo simulations of Ps-$p$ dynamics in a linearly polarized infrared field. We do not observe a drastic enhancement of the cross sections similar to that predicted before in laser-assisted electron bremsstrahlung and electron recombination since in the present charge-transfer process the Coulomb focusing effect is absent. Still we see a substantial enhancement up to a factor of 3 in the energy range between ${10}^{-4}$ and 0.1 eV for the field of intensity between 10 $\mathrm{MW}/{\mathrm{cm}}^2$ and 10 $\mathrm{GW}/{\mathrm{cm}}^2$. The effect depends weakly on the orientation of the incident Ps velocity relative to the field polarization vector. Rydberg states of the produced hydrogen atoms whose orbits are close to circular can survive against ionization by laser field and decay spontaneously to lower states. This is favorable for spectroscopic studies of antihydrogen atoms.

We exploit techniques for generating vortices and controlling their interactions in an optical beam in a nonlinear atomic vapor. A precise control of the vortex positions allows us to observe strong interactions leading to vortex dynamics involving annihilations. With this improved controlled nonlinear system, we get closer to the pure hydrodynamic regime than in previous experiments while a wavefront sensor offers us a direct access to the fluid's density and velocity. Finally, we developed a relative phase shift method which mimics a time evolution process without changing nonlinear parameters. These observations are an important step toward the experimental implementation of a two-dimensional turbulent state.

In this paper, we investigate the interplay between the second- and the third-order nonlinearities in lithium-niobate waveguides with strong waveguide dispersion using uniform and linearly chirped poling patterns at input powers in the picojoule range. We implement the accurate unidirectional pulse propagation model to take into account all the possible nonlinear interactions inside these structures. In particular, the poling period is designed to quasi-phase-match single and multiple sum- and difference-frequency generation processes. We show how the poling period can be used as an additional degree of freedom to transform the output spectra of chip-based nonlinear waveguides in an unprecedented way.

We show theoretically and numerically that a time-reversed replica of the pump pulse envelope in a frequency converted signal can be achieved using a nonlinear time lens realized with an accelerating spatiotemporal quasi-phase-matching (QPM) modulation. The nonlinear process depends on a suitable combination of the input and output dispersion and acceleration rate of a quadratic spatiotemporal QPM modulation.

Manipulating many-body quantum systems is a challenge. A useful way to achieve it would be to entangle the system to a diluted system, with a small particle number. Preparation of such entangled states can be facilitated as the ground state of a many-body Hamiltonian or the steady state of a many-body open quantum system. Here we study two-site lattice models with a conserved boson number, biased to display a large occupancy in one of the sites. The von Neumann entanglement entropy as well as the logarithmic negativity show a typical power-law decay in $R$, the occupancy ratio between the two sites. These results imply that it is feasible to entangle a large many-body system to a single atom, as recently reported experimentally.

We investigate the problem of reversing quantum dynamics, specifically via optimal Petz recovery maps. We focus on typical decoherence channels, such as dephasing, depolarizing, and amplitude damping. We illustrate how well a physically implementable recovery map simulates an inverse evolution. We extend this idea to explore the use of recovery maps as an approximation of inverse maps, and apply it in the context of non-Markovian dynamics. We show how this strategy attenuates non-Markovian effects, such as the backflow of information.

Encoding is an indispensable procedure in general phase measurement, and it is usually performed with a deterministic unitary transformation between the initial probe state and the final state. In order to improve the measurement precision, many studies focus on the optimization of the initial probe state. In this paper, we propose a scheme of subtracting one photon from the output state of an SU(1,1) interferometer. In addition to improving the output state, we find that this scheme can be used to optimize the encoding procedure. The performance of this type of optimization is only strong when the phase-sensitive negativity is induced in the Wigner function of the equivalent probe state. If a nearly perfect single-photon detector is used for the single-photon subtraction operation, the phase sensitivity within a narrow phase range can surpass $1/\left(\sqrt{\nu }N\right)$, where $N$ is the mean number of photons inside the SU(1,1) interferometer, and $\nu$ is the number of copies of the Gaussian probe state.

We demonstrate radiative force deflection by using an optical cycling of the $X{}^2{\mathrm{\Sigma }}_{1/2}^{+}-A{}^2{\mathrm{\Pi }}_{1/2}$ electronic transition in diatomic molecule magnesium monofluoride (MgF). For the (0,0) and (0,1) bands of the electronic transition, the Franck-Condon factors—obtained by the dispersed laser-induced fluorescence spectrum—are $f_{00}=0.972$ and $f_{01}=0.028$, which suggests that the vibrational branching is quasiclosed. Furthermore, the dark Zeeman sublevels are destabilized by applying an external magnetic field. The cycling fluorescence is clearly observed to reveal that the molecular beam is deflected by 4.9 mm via scattering $\sim 200$ photons per molecule. This work is encouraging toward laser cooling and magneto-optical trapping of MgF molecules.

A challenging effort is under way to understand the essence of the quantum size effect of two-dimensional materials in order to achieve the ultimate goal of arbitrarily tailoring their properties in the near future. Here we present experimental and theoretical study of resonant neutralization of low-energy alkali-metal ions on clean and graphene-covered polycrystalline copper surfaces. The ion neutralization strongly depends on the number of graphene layers, and it gradually saturates for three to five layers of graphene. This result is consistent with that for the graphite surface. The neutral fraction for the clean polycrystalline copper surface is found to be significantly higher than that for the graphene-covered surface, which is not consistent with known regularities. We quantitatively explain those observations through the small energy level width of resonant electron transfer that is determined by the special electronic structure of graphene layers. This finding indicates that resonant neutralization spectroscopy has promising applications in the detection of the quantum size effects of two-dimensional materials at an atomic layer level.

Self-trapped droplets stabilized by quantum fluctuations have been experimentally realized in dipolar gases and binary boson mixtures. In this paper, we propose spinor Bose gases as another candidate for droplet formation. For spin-1 gas, we find that spin fluctuations give a dilute but self-trapped state for two different order parameters where the mean-field picture predicts collapse. A polar droplet phase can be stabilized by spin fluctuations for both antiferromagnetic and ferromagnetic spin-dependent coupling. An antiferromagnetic droplet phase can be stabilized similarly with a negative quadratic Zeeman shift. Furthermore, the beyond mean-field energy of the system depends on the quadratic Zeeman coupling, which provides a mechanism to tune the droplet formation and its density. We discuss the parameters necessary for the experimental realization of such spinor droplets.

We unveil that even an infinitesimal deviation of the initial state from the eigenstates of the initial Hamiltonian can yield a significant change in the geometric phase accompanying adiabatic evolution without degeneracies of the energy levels. This leads to the counterintuitive result that the values of two geometric phases computed from the general definition of the Berry phase [Samuel and Bhandari, Phys. Rev. Lett. 60, 2339 (1988)] can dramatically differ from each other in the adiabatic limit even if their evolution paths are sufficiently close in a pointwise manner. The result of this work indicates that the widely accepted theory of geometric phases is not very consistent in the context of adiabatic evolution involving superposed eigenstates.

A broad class of informationally complete symmetric measurements is introduced. It can be understood as a common generalization of symmetric, informationally complete positive operator-valued measures and mutually unbiased bases. Additionally, it provides a natural way to define two more families of mutually unbiased symmetric measurement operators in any finite dimension. We show a general method of their construction, together with an example of an optimal measurement. Finally, we analyze the properties of symmetric measurements and provide applications in entropic relations and entanglement detection.